Galactic Origin For 62M-Year Extinction Cycle? 221
Hugh Pickens writes "Cosmologist Adrian Mellott has an article in Seed Magazine discussing his search for the mechanism behind the mass extinctions in earth's history that seem to occur with a period of about 62 million years. Scientists have identified nearly 20 mass extinctions throughout the fossil record, including the end-Permian event about 250 million years ago that killed off about 95 percent of life on Earth. Mellott notes that as our solar system orbits the Milky Way's center, it oscillates through the galactic plane with a period of around 65 million years. 'The space between galaxies is not empty. It's actually full of rarefied hot gas,' says Mellott. 'As our galaxy falls into the Local Supercluster, it should disturb this gas and create a shock wave, like the bow shock of a jet plane,' generating cascades of high-energy subatomic particles and radiation called 'cosmic rays.' These effects could cause enhanced cloud formation and depletion of the ozone layer, killing off many small organisms at the base of the food chain and potentially leading to a population crash. So where is the earth now in the 62-million year extinction cycle? '[W]e are on the downside of biodiversity, a few million years from hitting bottom,' writes Mellott."
Not news (Score:3, Informative)
Clouds? (Score:5, Informative)
So the milky way is falling sunny-side up? (Score:1, Informative)
from TFA: It turns out that the biodiversity minima of the 62-million- year cycle happens when the Sun is âoebobbed upâ on only one side of the galaxy, when the solar system is on the diskâ(TM)s upper, âoenorthâ side...These [cosmic rays] should be showering the north side of the galaxyâ(TM)s disk. We are protected by the galactic magnetic field, much as the Earthâ(TM)s magnetic field protects our planet. When we rise to the north side, we are less protected.
Re:Not a new idea (Score:5, Informative)
It's unlikely. Another star (the size of our Sun) needs to pass about 2 light-years near the Sun to significantly disturb the Oort cloud. And Sun-like starts are not that common.
However, Sun's gravitational field is so weak in the Oort cloud that even _Galactic tides_ can eject objects from it. Few years ago I helped my friend to write a computer simulation of this for his thesis.
Comment removed (Score:3, Informative)
Re:So what keeps the globular clusters alive? (Score:2, Informative)
Re:Clouds? (Score:5, Informative)
A recent paper shows that this may indeed by the case [uwaterloo.ca]
Given that Svensmark's team has been granted an experiment slot at CERN [web.cern.ch], at least many of those in the Physics community believe it's a plausible hypothesis. There is research out there demonstrating some causal link between cloud cover and Cosmic Rays. [harvard.edu] Science is all about reaching beyond what is known. It would be pretty a pointless exercise otherwise.
Adrian Melott (Score:2, Informative)
Not to be anal, but his name is spelled Adrian Melott , with one L. This spelling will help if you google his name.
I attend the University of Kansas (where he teaches), and know this guy is associated with some pretty far out ideas.
Re:Not a new idea (Score:3, Informative)
Unlikely? With, *currently*,
- Alpha Centauri [wikipedia.org] A+B massing 1.100 + 0.907 solar masses 4.365 ly away, and
- Sirius [wikipedia.org] A+B massing 2.02 + 0.978 solar masses 8.6 ly away,
I don't see what's so unlikely about having stars the size of our Sun passing within 2 light-years of the Sun once every 62 My.
Re:Clouds? (Score:4, Informative)
All such theories should be described as tentative, in the absence of solid physical evidence (i.e. not just correlation). The CERN experiment will at least show what and how cloud condensation nuclei can be generated by Cosmic Rays. This may, or may not, be the start of a paradigm shift in Climate Science. We will wait and see.
And also: (Score:3, Informative)
Nightfall [wikipedia.org] (Isaac Asimov, 1941, and Isaac Asimov & Robert Silverberg, 1990)
Re:What a f**king dick (Score:4, Informative)
>> IDNTRTFAWIDTBYDE (i don't need to read the f**king article when i'm drunk too because you didn't either)
I finally realized that, today, for the first time I've been on Slashdot too long.
I was able to understand your acronym without the explanation just by looking at the letters.
OMG.
Re:Not a new idea (Score:2, Informative)
though I think the theory than was than the gravitational field of passing stars was changing the orbit of comets in the Oort cloud and causing comet impacts.
So in other words, it is a new idea, as the one you read about was a different idea.
Not fault of galactic arms (Score:3, Informative)
Spiral Arms Did Not Cause Climate Change on Earth
A new map of the Milky Way galaxy proves that the sun's motion through the spiral arms could not have caused a well-known climate-change cycle.
http://www.technologyreview.com/blog/arxiv/23763/ [technologyreview.com]
Re:Skeptics (Score:2, Informative)
From their site:
"CNSNews.com is an alternative to the liberal media, focusing on stories that are unreported, under-reported, or misreported by the mainstream press."
They're pretty open about declaring their far-right bias, at least, but I wouldn't see them as a good source if you're interested in facts rather than worldview confirmation.
Although if you actually believe that there's a chance of the USA breaking up in the forseeable future you may be immune to facts.
Re:Just no (Score:5, Informative)
Is it really flamebait to say that humans are the most likely cause of biodiversity downfall?
No; it's only considered flamebait in political/religious circles. ;-)
In scientific circles, it's conventional to attribute most of the current extinction event to human activity. Thus, we don't really know when humans first arrived in the Americas, and there are estimates at high as 30,000 years ago for the first. However, it does seem fairly clear that humans were rare on those continents before about 12,000 years ago, when there was a huge increase in the human population. At the same time, large numbers of large animal species went extinct. Some of those would have died out anyway, but the mass extinction is generally attributed to humans. After all, if you introduce a new major predator, you'd expect that the sort of prey it likes (large, meaty critters in this case) would start to disappear.
So the human-caused extinction has long been the default hypothesis. There are other possibilities, but if you want to argue for them, you should have some pretty good evidence, and such evidence doesn't seem to exist. Death at the hands of a new, powerful predator is just too reasonable to be dismissed without evidence, and it quite properly the primary hypothesis when there is evidence of such a predator. And, unlike in political discussions, there is rather little scientific argument about this. Rather, there are lots of scientists looking for evidence wherever they can find it. Other contributing factors have been reported, but so far nothing much that seriously challenges the primary hypothesis.
(Actually, there is a good recent example of the opposite process. Starting about 500 years ago, there was a mass extinction of humans in the Americas. It is common to attribute this to the introduction of a different human subspecies that had better weapons. But we have the evidence, and it shows that weaponry was a minor factor in the extinction, and only in the eastern coastal areas. It turns out that most of the people in the interior died from the diseases that the new humans unknowingly brought along, long before the newcomers reached the interior. Both groups of people attributed the plagues to acts of various gods, since neither had any understanding of microorganisms at the time. It wasn't until the 1800s that "germs" were understood, and the newcomers started using biological warfare in a controlled fashion against the original inhabitants. This produced a second extinction event, but it was much smaller than the one in the 1500s.)
(And it'll be interesting to see whether this gets any "flamebait" mods. There's gotta be at least a few people who'll read it that way. I've already got both "flamebait" and "insightful" for one post; now I'm trying for "flamebait" + ("informative" || "insightful") + "funny". ;-)
20 Million Years Late... (Score:4, Informative)
... and a dollar short.
This is twice in a week that someone has made assertions about mass extinctions, and both times their (different) numbers don't match the commonly accepted numbers http://en.wikipedia.org/wiki/Milky_way [wikipedia.org] . (No, the Big W is not necessarily authoritative, but the sources referenced are.)
The solar system orbits the galactic center in 220 Myr. It oscillates through the galactic plane 2.7 times per orbit. That's a period of 81.5 Myr, and each crossing at half-period being 40.75 Myr. I doubt anyone would consider that an acceptable error margin.
Furthermore, the matter density in the galactic plane oscillates with a period 1/2 that of the galactic rotation, expanding out from the center in waves (density wave 25 Myr; spiral structure 50 Myr). Passing through the plane would have little effect unless these two coincide.
Re:Heard a similar (Score:2, Informative)
Re:Mayan Calendar (Score:3, Informative)
Wikipedia is your friend. [wikipedia.org]